Aiding auto-ignition in tar sand formation

ABSTRACT

Control of in situ auto-ignition of heavy oil in a tar sand formation is achieved by insuring an amount of liquid water in the formation such that oxygen consumption is increased when air or oxygen is injected thereinto. Oxidation rate is increased and therefore the time required to reach auto-ignition is reduced. The method is applicable to operations such as in situ drive combustion. Water, hot water, or steam can be used. Both oil-wet and water-wet sands exhibit increased oxygen consumption over sands not containing a degree of water saturation. A water saturation of say 15 percent in a 45 percent porosity sand results in about a 2 1/2 times increase in O2 consumption over that of dry sand. With injected water, raising the total formation of water to about 20 percent, the temperature after 1,000 hours of air injection was 180* F. whereas without water injection the temperature of the dry sand was only 96* F. in an experiment applied to Asphalt Ridge tar sand.

United States Patent Peacock et al. [451 Aug. 1, 1972 [5 AIDING AUTO-IGNITION IN TAR SAND Primary Examiner-Stephen J. Novosad FORMATION Attorney-Young and Quigg [72] Inventors: Dixon W. Peacock- Riley B. Needham, both of Bartle sville, Okla. [571 ABSTRACT Parole Control 'of in situ auto-ignition of heavy oil in a tar [73] sslgnee' Phillips um Company sand formation is achieved by insuring an amount of Filed: i 10, 1970 liquid water in the formation such that oxygen con- 1 A L N 27 210 sumption is increased when air or oxygen is injected [2 1 pp 0 thereinto. Oxidation rate is increased and therefore the time required to reach auto-ignition is reduced. [52] US. Cl. ..l66/26l The method is applicable to operafions such as in situ [51] Int. Cl. ..E21b 43/24 drive combustion water hot water or steam can be of Search used. Both oiLwet and waepwet Sands exhibit creased oxygen consumption over sands not contain- [56] Reierences Cited ing a degree of water saturation. A water saturation of UNITED STATES PATENTS say 15 percent in a f5 percent porosity sand results in about a 2% times increase in 0, consumption over gla that of dry sand. With injected water, raising the total formation of water to about 20 percent, the tempera- 3,l96,945 7/1965 Craig et a]. mm after 1,000 hours of air injection was 0 R 2 g s' g etal 4 whereas without water injection the temperature of g 6/1970 et a] 6,261 x the dry sand was only 96 F. in an experiment applied 3,5 5, en et to Asphalt Ridge tar sand Gates, C. F. et al., Better Technology Opens Way For More Thermal Projects In Oil & Gas 1., July 13, 1964 p. 74 relied on.

WATER WET SAND 2o WATER 8. OIL WET SAND DRY SAND CUMULATIVE OXYGEN CONSUMPTION, ml/g OIL G TIME,HOURS PAIENTEmus 1 m2 DRY 3960 HRS 2000 HRS SHEET 1 BF 3 2o 90 WATER 3220 HRS 3000 HRS "2000' HRS .IOOO HRS 1000 HRS o I00 200 0 I00 200 RADIUS; FEET RADIUS, FEET INVENTORS AIDING AUTO-IGNITION IN TAR SAND FORMATION This invention relates to aiding auto-ignition of a heavy oil in a formation.

In one of its concepts the invention reduces the time taken for auto-ignition in a tar sand by injecting into the fonnation water.

We have found that injecting water into a heavy oil or tar sand such as Asphalt Ridge tar sand near Vernal, Utah reduces substantially the time taken for auto-ignition of the hydrocarbon in the sand. It appears that injection of the water into the sand considerably increases the difiusion of oxygen through the sand and into the oil thereby increasing the rate of oxidation. Upon consideration it appears that the diffusion rate of oxygen through water is approximately 100 times that of oxygen through oil.

Further, we have conceived that where liquid water is already present in a formation which it is desired to ignite initial air injected into the formation will move the water in the formation back into the formation away from the oil leaving theoil in the formation in a water-wet condition. As more air is injected the diffusion of oxygen above discussed is now obtained and the time'taken to reach auto-ignition is reduced. Thus a reservoir that is no longer economic to produce because of water encroachment during a primary production can be air injected according to the invention following which it can be produced by in situ combustion in a time shorter than otherwise and of course there is no need to efiect any other water removal operation other than air injection which accomplishes both the water displacement and the ignition. In some cases the concepts of the invention are applicable to counterflow or indirect drive in situ combustion.

It is an object of this invention to produce a tar sand as by in situ combustion. It is a further object of the invention to produce a crude oil by auto-ignition of a tar sand containing same. It is a further object of this invention to provide for an in situ drive combustion within a formation. Still further is an object of the invention to eliminate uncertainty, tedium and expense involved in artificially igniting reservoirs, especially deep reservoirs. A further object of the invention is to increase the rate of oxidation of a tar sand and therefore to decrease the time required for auto-ignition of the reservoir.

Other aspects, concepts and objects of the invention are apparent from a study of this disclosure, the drawing and the appended claims.

According to the present invention there is provided a method of increasing the rate of oxygen absorption and therefore oxidation of a hydrocarbon oil in a tar sand which comprises providing liquid water in said sand in an amount in the approximate range of from about to about 80 per cent of the porosity of said sand and then injecting an oxidant into said sand.

Still according to the invention water is injected into a tar sand of low water saturation to establish the desired water saturation.

Further still according to the invention the water injected into the reservoir can be in the form of hot water or steam.

Still further according to the invention air can be injected into a watered out reservoir or into a reservoir that is no longer economic to produce because of water encroachment during primary production to create the condition in which there remains a water-wet oil formation which can then be auto-ignited due to the increased oxygen absorption and therefore rate of oxidation to reach auto-ignition in a relatively short time and without use of expensive artificial ignition methods.

The methods for injecting water and/or air, or for that matter hot water or steam are well known in the art and are omitted for sake of simplicity. Suflice to say that the usual piping, valving, pumping means and control means are provided so that the water or air or oxygen can be injected into the bore hole and by means of the bore hole into the formation at a desired depth.

Referring now to the drawing,

FIG. 1 shows dramatically the increase in temperature with respect to time in Asphalt Ridge tar sand at a depth of about 2,800 feet.

FIG. 2 shows the eflect on oxygen consumption related to Asphalt Ridge tar sand core material at 120 to 140 F. and under 1,000 psig.

FIG. 3 shows the effect of water on oxygen consumption related to Danglemayer crude on extracted Morichal sand at 120 F. and 1,000 psig.

Referring now to FIG. 1 (which is curves produced I from heat transfer calculations using laboratory test data used in producing the curves in FIG. 2), it will be seen that up to a radius of approximately 50 feet the sand containing 20 per cent of water had reached almost 500 F. after approximately 3,220 hours whereas even after almost 4,000 hours the dry sand had reached a temperature, approximated, of only about 345 F at best. At 3,000 hours the temperature of the water injected sand was approximately 435 whereas for the dry sand at the same elapsed time ofair injection the temperature was only about! 25 F. FIG. 1 shows therefore the dramatic decrease in time required for raising the temperature of the oil bearing formation upon air injection to produce auto-ignition when the formation is injected with water or at least the oil bearing formation is wetted with water at the time that the air is injected.

Dry sand referred to in this discussion refers to an oil-containing sand'in which no water is present, in contrast to water-wet oil sand which refers to a sand containing oil into which water has been injected.

Referring now to FIG. 2, again the dramatic changes obtained by water injection are illustrated in terms of cumulative oxygen consumption in milliliters per gram of oil. The legend on the drawing is self-explanatory. It will be seen that with water-wet sand a relatively high oxygen consumption is obtained. With water and oilwet sand, the tested sand containing 5 per cent oil and 5.5 per cent water by weight containing 1,800 ppm sodium chloride, the cumulative oxygen consumption was higher than that for dry sand containing oil.

The available information on salt water saturation in the Asphalt Ridge formation is 25 percent, with the salinity of 1,800 ppm NaCl. Therefore, the mixture used for test was 5 weight .per cent Asphalt Ridge tar and 5.5 weight per cent water containing 1,800 ppm NaCl on Asphalt Ridge sand. Oxidation runs were made at temperatures of F., F and F., at air pressures of 500 psig and 1,000 psig. The oxidation rate at 90 F. with the water phase present was about 8 times that of the dry system and remained essentially constant with time. The air pressure had little eflect between 500 and 1,000 psig. At 120 F. the oxidation rate with water added was sharply increased during the early stages of the process. Further, both the rate and level of cumulative oxygen consumption at 140 F. was only slightly higher than at 120 F. In FIG. 2 curves 1, 2 and 3 all were made up of Asphalt Ridge core material containing per cent oil and 5.5 per cent water solution of 1,800 ppm of sodium chloride simulating the oil and water conditions of Asphalt Ridge tar sands. Curves 4 and 5 were made with no water present in the core with only 5 per cent oil being placed in the sand. These two curves are for a dry sand condition.

. Although the rate of oxidation of the oil depends on. whether the sand is partially oil-wet or water-wet (oil added first or second in tests) the presence of water greatly increases the rate of oxidation of the crude whencomparedto that of the dry tar sand.

Referring again to FIG. 2, it will be seen that whereas thedry tarsand after 500 hours show a consumption of approximately 8 milliliters or less at 120 F. of oxygen per gram of oil (lower curve)-the time taken to reach this consumption with water present was of the order of 110 hours at l F. I

Referring now to FIG. 3, the dramatic changes obtained by water injection are illustrated in terms of cumulative oxygen consumption in milliliters per gram of oil. The legend is self-explanatory. It will be seen that with water-wet sand a relative high oxygen consumption is obtained. With water and oil-wet sand, the tested sand containing 5 per cent of crude oil and 5 per cent of water by weight, the cumulative oxygen consumptionwas somewhat lower than that for the water-wet sand but still considerably higher than that for the dry sand. Thus the effect of water saturation for both oilwet and water-wetsands is set forth.

Again referring-to FIG. 3'it will be seen that where as the dry sand afier 500 hours shows a consumption of approximately 12% milliliters of oxygen per gram of oil (lower curve) the time taken to reach this consumption with water present (middle curve) was of the order of 150 hours. With water-wet sand in about the same time, i.e., 150 hours, 20 milliliters per gram of oil of oxygen has been absorbed or consumed.

In obtaining the above data the low temperature oxidations were carried out in 150 ml double ended stainless steel bombs. The bombs were fitted with brass fittings to allow gas samples to be taken periodically for chromatographic analysis of oxygen, nitrogen and carbon dioxide, starting after approximately one and onehalf hour of heating under pressure. The sand-oil mixture was prepared by kneading together weight amounts of sand and oil in a sealed plastic bag until the mixture was homogeneous. The porosity of the sand-oil mixture when packed into thebomb was approximately 38 per cent. Seven and one-half weight per cent of oil in this pack resulted in an oil saturation of approximately 40 per cent. Five per cent by weight of oil was used resulting in an oil saturation of less than 40 per cent. The weight of oil in the bomb was obtained from :the difference in weight of theempty bomb and the filled bomb, and from the weight of oil in the oil-sand mixture. Afier the weight of the oil in the bomb was determined the bomb was filled with air from a compressed air cylinder at room temperature such that the mixed with the oil and sand was determined by the same method of mixing and weighing as for the mixing of oil in the sand.

The invention is particularly applicable to the injection of water ahead of or even behind air in a direct drive in situ combustion process. An advantage of the presence of water in the reservoir prior to air injection is the added volume of water and steam flood resulting from heating of the injected water that will precede the 20 fire front, aiding in displacing the oil. In general the invention is particularly applicable to heavy oils having an API gravity of 20 and lower.

One skilled in the artin n of this disclosure having studied the same will be able to select by routine tests the rates of water and/or air injection and the pressures at which these are to be accomplished'depending upon the nature of the reservoir or formation and its depth and the natural or ambient temperatures and pressures there prevailing.

Although an explanation has been given for the increased oxygen consumption and therefore decreased time to reach auto-ignition we do not intend to be bound thereby. Clearly the results obtained upon operating as herein described demonstrate the invention.

EXAMPLE In a single test a homogeneous sample of the Asphalt 0 Ridge core material was separatedinto two portions.

To one portion 3.4 per cent by weight of water was added and made homogeneous by mixing. Oxidation runs, at 120 F. and 1,000 psig, were made on these two portions of the Asphalt Ridge core material. I

The oxygen consumption at about 550 hours ha reached approximately 22 milliliters per gram of oil in the water-wet core material whereas at this time in the non-wet material it had reached from about 7% milliliters of oxygen per gram of oil. Further, the initial absorption or consumption of oxygen in the water-wet core material increased considerably more rapidly at the outset than that of the non-wet sand.

Generally, the rate of oxygen consumption per gram of oil present for the core material plus water was approximately 2% times that of the dry core materiaLThe dry core material contained approximately 0.2 weight per cent water and its oxidation rate reproduced data taken previously on Asphalt Ridge tar sand core material. The 3.4 weight per cent water added in this test was equivalent to a water saturation of 14 per cent in the 45 per cent porosity sand pack. Water saturation in the Asphalt Ridge fonnation is about 25 per cent on the basis of logs.

Reasonable variation and modification are possible within the scope of the foregoing disclosure, the drawing and the appended claims to the invention the essence of which is that water-wet oil bearing formation or sand will absorb oxygen considerably faster than non-wet sand formation and therefore that the time taken to reach auto-ignition is considerably reduced.

We claim:

l. A method of increasing the rate of oxidation and therefore decreasing the time taken to reach auto-ignition of a hydrocarbon bearing tar sand formation without preheating the same which comprises providing liquid water in said tar sand formation in an amount sufficient to increase the oxygen consumption of the formation and injecting air or other oxygen bearing gas into the formation and wherein the amount of water in the formation at the time of air injection is adjusted to be such in the approximate range of from about to about 80 per cent of the porosity of the oil bearing sand formation, that auto-ignition is reached in a substantially reduced time of injection of said air or other oxygen bearing gas than in the absence of said amount of water.

2. A method according to claim 1 wherein the formation is a heavy tar-like oil containing sand and the oxygen bearing gas is air.

3. A method according to claim 1 wherein a direct drive in situ combustion is initiated by auto-ignition by first providing the water in quantity sufficient to wet the sand.

4. A method according to claim 1 wherein the water is first injected and then the oxygen bearing or oxidizing gas in injected.

I t I t 

2. A method according to claim 1 wherein the formation is a heavy tar-like oil containing sand and the oxygen bearing gas is air.
 3. A method according to claim 1 wherein a direct drive in situ combustion is initiated by auto-ignition by first providing the water in quantity sufficient to wet the sand.
 4. A method according to claim 1 wherein the water is first injected and then the oxygen bearing or oxidizing gas in injected. 